The invention relates to the field of x-ray imaging systems, and in particular to an x-ray imaging system that employs digital tomography and a rapidly moving x-ray source.
The original tomography systems employed an imaging technique wherein an x-ray source and a film mounted below the object under inspection (typically a person) were moved in opposed directions along prescribed paths so that only one plane of the object under inspection is in focus at all times. The motion of the x-ray source is in a plane parallel to the plane of the film. Structures in a slice parallel to the film plane projected onto the film in the same relative positions throughout the entire examination. All other planes above and below projected in different positions of the film at different times through the motion, and therefore were blurred. This system allowed the production of only a single slice of the object under inspection with each exposure to the cone of x-rays.
With the development of scintillating materials, solid state detectors and digital computers, linear digital tomography systems were developed using an x-ray source and collimator emitting a fan beam of x-rays incident on a line of detectors. The fan beam is translated along the line of detectors by physically moving the source, and every detector is sampled as the fan beam translates. It is then possible to later choose the proper set of detectors to read which will focus on a single line, parallel to the line of detectors. Because all of the data is stored, this line can be chosen at any distance between the x-ray source and the line of detectors.
A limitation of this prior art technique is that the x-ray source must be moved mechanically, and therefore slowly in order to translate the beam along the line of detectors. Thus, each line of data requires mechanical motion of the rather heavy x-ray source along the full dimension of the object being imaged. For example, if the motion of the source were to be accomplished in 1 second, and if one wished to have an image with 1000 pixels in the direction perpendicular to this motion, it would take 1000 seconds to complete an image. In addition, the complexity of such a mechanical moving system is considerable.
Therefore, there is a need for a x-ray imaging system, such as for example a digital tomography system, which rapidly positions the x-ray beam without having to mechanically scan/move the x-ray source over the object under inspection.
Briefly, according to an aspect of the invention, a digital tomography system includes an electron source that provides a beam of electrons, and an electromagnet assembly that receives said beam of electrons and is configured and arranged to direct the beam of electrons along a selected path, wherein the assembly provides a redirected beam of electrons. The system also includes a target that is struck by the redirected beam of electrons and generates a cone of x-rays, and a slit collimator that receives the cone of x-rays and generates a fan beam. A first line of detectors is positioned to detect x-rays that pass through the object under inspection, and provide sensed signals indicative thereof to a controller that receives the sensed signals and forms a displayable image of a selected plane through the object under inspection.
The digital tomography system can be configured and arranged for various applications including for example, medical applications and for contraband detection. For example, in a medical application the electron source would be rather low energy, such as a 150 KeV x-ray tube. In a contraband detection suitable for the inspection of cargo pallets and trucks, the electron source would be a rather high energy source, such as for example greater than one MeV. In addition, the system may be configured either as a stationary system or as a mobile system (e.g., mounted on a truck).
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings.